1. Field of the Invention
This invention relates to a data storage system used as an external storage apparatus for a computer and to a log data equalization control method for a storage control apparatus, and in particular relates to a data storage system having, among numerous disk devices, disk devices used by users and a system disk device used by the apparatus, and to a log data equalization control method for a storage control apparatus.
2. Description of the Related Art
As data has assumed various electronic forms in recent years and has come to be handled by computers, independently of host computers executing data processing, data storage apparatuses (external storage apparatuses) capable of storing large amounts of data efficiently and with high reliability have become increasingly important.
As such data storage systems, disk array apparatuses having large-capacity disk devices (for example, magnetic disk and optical disc devices) and disk controllers used to control such large-capacity disk devices have come into use. Such a disk array apparatus has memory serving as a disk cache. By this means, when read requests and write requests are received from a host computer, the time required to access data can be shortened, and enhanced performance can be achieved.
In general, a disk array apparatus has a plurality of principal units, that is, a channel adapter which is a portion for connection to host computers, a disk adapter which is a portion for connection to disk drives, a memory having a cache area, a control portion which serves to control the cache memory, and large-capacity disk drives.
FIG. 25 explains the technology of the prior art. The disk array apparatus 102 shown in FIG. 25 has two control managers (memory, including cache memory, and a control unit) 10 and each control manager 10 is connected to channel adapters 11 and disk adapters 13.
The two control managers 10, 10 are directly connected by a bus 10c so as to enable communication. The channel adapters 11 are connected to host computers (not shown) by for example fiber channel or Ethernet (a registered trademark). The disk adapters 13 are connected to each of the disk drives in disk enclosures 12 by, for example, fiber channel cable.
A disk enclosure 12 has two ports (for example, fiber channel ports); these two ports are connected to different disk adapters 13. By this means redundancy is imparted, and fault tolerance is improved. (See for example Japanese Patent Laid-open No. 2001-256003)
In such a large-capacity data storage system, a large amount of information (called system information) is necessary for control by controllers (control units, channel adapters, disk adapters and similar). For example, system information includes firmware necessary to operate controllers, backup data for the apparatus configuration, and log data for various tasks and threads.
The firmware is control programs for controllers; in particular, in a disk array (RAID configuration), numerous control programs are necessary. Backup data for the apparatus configuration is data used to convert from host-side logical addresses to physical disk addresses and is necessary a large amount of data, according to the number of disk devices and number of hosts. Log data is state data for each task and thread, used for fault recovery and fault prevention, and also constitutes a large volume of data.
Such system data is generally stored in a nonvolatile large-capacity storage device. In the prior art, as shown in FIG. 25, a portion of the disk drives 120 in the disk enclosure 12 connected by cables to the disk adapters 13 was used for storage of such data. A disk drive which stores this system data is called a system disk.
That is, a portion of the numerous disk drives connected to controllers are used as system disks, and the other disk drives are used as user disks. As a consequence of this conventional technology, as indicated in FIG. 25, any of the controllers 10 can access system disks 120.
However, in addition to redundancy, in recent years storage systems have been required to continue operation even upon occurrence of a fault in any portion of the system. In the technology of the prior art, if a problem arises in the path between a controller and a disk enclosure, such as for example between a disk adapter and a disk enclosure, reading and writing of a system disk 120 can no longer be executed.
Consequently even if the controller and other paths are normal, the controller cannot read firmware or apparatus configuration backup data from the system disk, and operations using other routes become difficult. Further, the controller cannot read or write log data to and from the system disk, impeding analysis upon occurrence of a fault and diagnostics for fault prevention.
Moreover, upon occurrence of a power outage it is necessary to switch to battery operation and to back up the data in the cache memory to the system disk. In the technology of the prior art, in such cases power must also be supplied to the disk enclosure, so that a very large battery capacity is required. Further, a comparatively long time is necessary to write backup data to a system disk via a disk adapter and cable, and when the cache memory capacity is large, a huge battery capacity is required.